1. Field of the Invention
The present invention relates to a disk recording system which allows data to be recorded in addition to already recorded data, and relates in particular to a disk recording system which ensures continuity of recorded data even when buffer underruns occur.
2. Description of Related Art
An optical disk recording system for recording data on a disk has been known in which a light beam is irradiated from an optical head onto a disk to change the reflectivity of a recording layer of the disk and thereby record data on the disk. Among such optical disk recording systems, a CD-R (recordable) drive of the CD (Compact Disc) family is a well known example in which a write-once medium that prohibits physical erasure of already recorded data is employed.
This write-once medium such as a CD-R, however, has a problem of buffer underruns in which a rate of data transfer for inputting data to a buffer does not keep up with a rate of data transfer for recording data on the medium, and this in turn leads to buffer underrun errors which cause the recorded data to be discontinuous. In the case of disc-at-once or track-at-once medium in which file groups to be written are previously designated, the recording medium cannot be used when such a buffer underrun error occurs.
Such buffer underrun error has become more likely to occur as the recording rate in CD-R drives has increased to be higher than 4 or 8 times the standard rate, and as personal computers are more often operated using multi-task functions. Accordingly, buffer underrun error is becoming a serious problem.
On the other hand, in a packet write system, data can be recorded by each packet, and therefore data recording is suspended until the data to be recorded fill the capacity of each packet, thereby preventing a buffer underrun error to occur. This is disclosed in, for example, Japanese Patent Registered Publication No. 2842262.
Here, it is necessary to ensure a compatibility between a CD-R drive and a CD-ROM drive such that data recorded on a disk by a CD-R drive can be reproduced by a CD-ROM drive. However, a problem of this compatibility is also unsolved because the packet write system is not always applicable to CD-ROM drives.
Further, when a CD-R drive records audio data corresponding to a CD-DA, a packet write system is not applicable to the CD-R drive due to a compatibility with a CD-DA player.
In a packet write system, because link blocks must be formed for connecting packets, there is also a problem of disk storage capacity.
According to the present invention, data to be added are synchronized by signal synchronizing means with data which have already been recorded on a disk and are then recorded at a recording start position on the disk detected by recording start position detecting means. Therefore, it is possible, when data recording is resumed, to record new data on the disk such that the new data are continuous to the data which have been recorded by the time data recording was interrupted. The added data can be reproduced in a manner continuous to the already recorded data without adoption of a packet write system. In this way, a disk recording system which can record data on a disk while ensuring a compatibility with other disk reproducing systems can be provided.
Further, if it is determined that buffer underruns are about to occur, data recording to a disk can be interrupted. Then, once it is determined that a situation in which buffer underruns are about to occur has been avoided, recording is resumed at a position from which new data can be recorded continuous to the last data which were recorded immediately before the interruption of data recording. Accordingly, a buffer underrun error by which data are recorded on a disk discontinuously can be prevented, and therefore the recorded data are reproducible, even on a disk reproducing system which can only read disks having continuously recorded data.
Further, in a disk recording system for recording data to which interleave processing is applied, data to be modulated are stored by an encoder when recording is interrupted to secure an interleave length necessary for new data to be inputted when recording is resumed. Therefore, even if data are interleaved, it is possible to modulate new data when recording is resumed such that they are continuous to the last data which have been recorded on a disk immediately before the interruption of recording.
Further, a recording start position may be detected by determining an address of the last frame of the data recorded on a disk while referring to the address stored immediately before the interruption of recording. Therefore, as a process previous to a detection of a position at which recording is resumed, it is possible to reliably and quickly detect the position of the last data recorded immediately before the interruption of recording, whereby the position where recording is resumed can be detected reliably and quickly.
In particular, the recording start position is detected by detecting an address of the data corresponding to one frame previous to the last frame of the data recorded immediately before the interruption of recording and counting channel bits using, as a reference, a frame synchronizing signal firstly detected after the aforementioned address is detected. Therefore, it is possible to additionally record new data on a disk in a manner continuous to the data recorded immediately before the interruption of recording.
Further, as an operation clock used for system control, a reproducing clock obtained by reproducing a pit signal may be used until the recording start position is detected, and when the recording start position is detected, the reproducing clock is switched to a recording clock used for data recording. Therefore, it is possible to make new data to be recorded on the disk synchronized with the data already recorded on the disk and to immediately initiate system control by means of a recording clock once a non-recorded region of the disk where a reproducing clock is not available is detected.